headers_check fix: powerpc, swab.h

fix the following 'make headers_check' warning:

  usr/include/asm-powerpc/swab.h:11: include of <linux/types.h> is preferred over <asm/types.h>
Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>

arch/powerpc/include/asm/swab.h

@@ -8,7 +8,7 @@
  * 2 of the License, or (at your option) any later version.
  */
 
-#include <asm/types.h>
+#include <linux/types.h>
 #include <linux/compiler.h>
 
 #ifdef __GNUC__